1. Field of the Invention
This invention relates to a center pivot irrigation system having the ability to irrigate the corners of the field being irrigated. More particularly, this invention relates to an improved method for controlling the application of chemicals beneath the center pivot portion of a corner irrigation system.
Even more particularly, this invention relates to a method for varying the speed of a center pivot irrigation machine equipped with a corner span to compensate for the change in area covered by the machine as the corner span moves away from the center pivot area and as it moves towards the center pivot area to maintain a uniform chemical depth beneath the center pivot portion of the machine.
2. Description of the Related Art
Conventional center pivot irrigation systems comprise an elongated main boom pivotally connected at its inner end to a center pivot structure and extending outwardly therefrom. The main boom of the conventional center pivot irrigation system is comprised of a plurality of pipes connected together in an end-to-end fashion which are supported upon a plurality of drive towers. In most conventional center pivot irrigation systems, the outermost drive tower or last regular drive unit (L.R.D.U.) is the master tower with the other drive towers being selectively driven in response to angular displacement of the boom section adjacent thereto.
In the early 1970s, corner systems for center pivot irrigation systems were developed to enable the corners of a square field to be irrigated. See, for example, U.S. Pat. Nos. 3,797,517; 3,802,726; and 3,902,668. Corner systems usually consist of an extension boom or arm, sometimes referred to as a corner span, which is pivotally connected to the outer end of the main boom and which is supported on at least one steerable drive tower. A guidance system is provided for guiding or steering the extension tower, and extension boom, out into the corners of the field as the main arm travels around the field. Perhaps the most popular method of guiding the extension tower is the buried wire system described in U.S. Pat. No. 3,902,668.
A plurality of spaced-apart sprinklers are provided on the main boom as well as on the extension boom. The sprinklers on the extension boom are not activated until the extension boom moves out into the corners of the field. Current center pivot irrigation systems with corner spans are used to apply chemicals to the area (field) beneath the system as the system moves around the area being chemigated. A problem associated with such chemigation is that the area being chemigated increases as the corner span moves away from the center pivot area and the area decreases as the corner span moves towards the center pivot area. The change in area being chemigated makes it difficult to maintain a uniform chemical depth beneath the center pivot portion of the machine.
In an effort to apply the chemicals uniformly beneath the center pivot portion of the system, the speed of the center pivot will be changed once (slowed down) as the corner span moves away from the center pivot area and the speed will be changed once (increased) as the corner span moves towards the center pivot area. This results in a large portion of the area beneath the center pivot machine to be either over chemigated or under chemigated.